# Science: Chemistry Year 10

Definitions
• Ion: An atom which is electrostatically charged
• Cation: Positively Charged ion
• Anion: Negatively Charged ion
• Valence shell: Outermost electron shell
• Octet: 8 electrons in the valence shell (2 if the element is Hydrogen or Helium)
• Catalyst: something that causes and/or speeds up chemical reactions
• Electron: negatively charged lepton
• exothermic: emits heat
• endothermic: absorbs heat
• Atomic number: number of protons
• Atomic mass: number of protons + number of neutrons
• Neutralisation: mixing an acid and a base to create water
• Corrosion: a gas or liquid chemically attacking an exposed surface
• Combustion: exothermic reaction between a fuel and oxidiser, which produces heat, light and gaseous products
• decomposition: when a single compound breaks down into two or more compounds
• oxidisation: corrosion reaction where the gas/liquid is Oxygen (O)
• Precipitation: formation of an insoluble solid when two soluble solutions are combined (product is known as a precipitate)
• Acid-Metal reaction: when an acid and metal react to produce a metallic salt and Hydrogen

## Periodic Table

• The periodic table is a table listing the fundamental building blocks of the universe: elements
• NOTE: ATOM and ELEMENT do NOT mean the same thing!
• An atom is a particle containing protons and electrons (and generally neutrons too)
• An element is a substance made out of the SAME TYPE OF ATOM
• An atom is the smallest sample of an element.
• Atoms have a nucleus (which contains their protons and neutrons) and orbiting shells (which contain electrons in fixed rings)
• Electron shells fill from the innermost available space:
• The first shell can hold a MAXIMUM of 2 electrons
• The second shell can hold a maximum of 8 electrons
• The third shell can hold 8 electrons until the fourth shell has 2 electrons, then another 10 (total of 18)
This concept is a bit confusing at first. Click here to see how it works - In the fourth period, Potassium has an electron configuration of Potassium is $2,8,8,1$ - Calcium is $2,8,8,2$ - Scandium is $2,8,9,2$ . After the 4th shell has 2 electrons, they begin to fill from the 3rd shell until Zinc, which fills the third shell to its capacity of 18 ( $2,8,18,2$ ). - After Zinc, electrons fill the outermost shell again until Krypton ( $2,8,18,8$ ), after which the fifth shell starts filling. - This trend occurs for shells 3/4 and 4/5.
- The fourth shell can hold 8 electrons until the fifth shell has 2 electrons, then another 10 (total of 18)

### Memorising the first 20 elements

• There is an easy way to memorise the first 20 elements, the Periodic Table Song
• You should memorise up to the first chorus (including the chorus) for Year 10 Chemistry. Year 11 and 12 Chemistry may require more.

### Representing Atoms

• There are several ways to represent an atom.
• The first way is the atom’s symbol.
• The atomic symbol is the one or two letter shortcode for the atom that can be seen on the periodic table.
• For example, Oxygen is represented as $O$ , while Calcium is $Ca$
• The first letter MUST be capital and the second letter (if present) MUST be lowercase. $ca$ , $CA$ or $cA$ for Calcium are all INCORRECT answers.
• Some elements have atomic symbols which somewhat match their name, such as $N$ for Nitrogen
• Others seem completely random, such as $Au$ for Gold. These tend to come from their Latin names (“Aurum” in the case of Gold)
• Another way is by writing out the ELECTRON CONFIGURATION.
• This is the filling order of the electron shells.
• For example, Hydrogen is $1$ , Oxygen is $2,6$ , etc.
• This method is not often used for naming an element, since electron configurations can change in Chemical Reactions.

## Chemical Reactions

• A chemical reaction is when the bonds between atoms are broken, formed or changed
• A chemical reaction has 2 parts: reactants and products
• Reactants are the substances BEFORE the reaction
• Products are the substances AFTER the reaction

### Law Of Conservation Of Mass

• The Law of Conservation of Mass states that:
Matter cannot be created nor destroyed, it can only be changed from one form to another.
- This means that in a chemical reaction, the total mass of the products MUST be the same as the total mass of the reactants. - For example, photosynthesis: - 6CO2 + 6H2O —> C6H12O6 + 6O2 - On both sides of the equation, there are: - 6 Carbon atoms - 6 Oxygen atoms - 12 Hydrogen atoms - This is known as a BALANCED EQUATION ### Law of Constant Proportions - The Law of Constant Proportions states that: -
A given chemical compound always contains its components in a fixed ratio.
• For example, in water, there will ALWAYS be two hydrogen atoms for every oxygen atom (H2O).
• If there were an equal number of hydrogen and oxygen atoms, then the substance would not be Water (H2O), instead it would be Hydrogen Peroxide (H2O2).

### Exothermic and Endothermic Reactions

• An EXOTHERMIC REACTION is a reaction that GENERATES heat/energy (exo-: outside, -thermic: heat)
• An ENDOTHERMIC REACTION is a reaction that REQUIRES heat/energy (endo-: inside, -thermic: heat)
• Sometimes, exothermic reactions require heat to start. However, their total energy output is GREATER than the total energy input

### Ionic and Covalent Bonds

• An IONIC bond is a bond between oppositely charged IONS (atoms with an unequal number of protons and electrons)
• Ionic bonds occur between a metal and a non-metal
• One atom will LOSE electrons, and the other will GAIN electrons so that both have a filled outer shell.
• For example, in $NaCl$ , The Sodium atom loses an electron and the Chlorine atom gains that electron. The two atoms are then electrostatically attracted together.
• A COVALENT bond is a bond where two non-metal atoms SHARE a pair of valence electrons
• An atom can have multiple covalent bonds. For example, carbon group atoms can have up to four covalent bonds
• Noble Gases (group 18) do NOT form bonds with anything (except in rare circumstances)
• Two atoms with a covalent bond can be said to be DIATOMIC

## VIDEO TUTORIAL: Lewis-Dot Diagrams (<8 minutes)

### Element Groupings

• The periodic table has several methods of being divided into categories.
• The first method is by PERIOD
• Elements in horizontal rows are in the same period.
• Each at the end of each period, the next electron shell begins to fill.
• The second method is by BLOCK
• Each block of the periodic table is determined by the electron orbitals which are filled in that block.
• Each block is named after the orbital which gets filled in that block
• The s-block is everything in columns 1 and 2, as well as Helium
• The d-block is everything from column 3 to 12, except the Lanthanides and Actinides
• The p-block is everything from column 13 onwards, except Helium
• The f-block is the Lanthanides and Actinides
• The third method is by GROUP
• Vertical columns of the Periodic Table are known as GROUPS
• Elements in the same group have similar properties
• Group 1: Alkaline Metals
• Group 2: Alkaline Earth Metals
• Group 3-12: Transition Metals
• Group 13: Boron Group
• Group 14: Carbon Group
• Group 15: Pnictogens
• Group 16: Chalcogens
• Group 17: Halogens
• Group 18: Noble Gases

##### Pranav Sharma
###### Site Owner

UNSW Student, site owner and developer.

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